1. Field of the Invention
This invention relates to filters, in general, and to a self-contained filter assembly for removing air, particles, and bacteria from a solution, in particular.
2. Description of the Prior Art
In the intravenous adminstration of liquid medications, parenteral solutions and the like, it is absolutely necessary that the solution being administered into a patient be free of entrained air, particulate matter, and bacteria. The prior art has come up with various filter arrangements to solve the problems associated with the removal of air entrained in a parenteral solution and also the removal of particulate matter and bacteria.
One class of filters, used to vent the air entrapped in the parenteral solution, employ various combinations of hydrophobic and hydrophilic filters. A hydrophobic filter is one which allows the passage of gas but does not allow the passage of liquid. A hydrophilic filter is one which allows the passage of liquid but does not allow the passage of gas. As examples of this type of filter arrangement, the following patents are considered exemplary:
U.S. Pat. No. 3,523,408 (Rosenberg); U.S. Pat. No. 3,631,654 (Riely); U.S. Pat. No. 3,803,810 (Rosenberg); U.S. Pat. No. 3,854,907 (Rising); U.S. Pat. No. 4,004,587 (Jess); U.S. Pat. No. 4,031,891 (Jess); and U.S. Pat. No. 4,116,646 (Edwards).
In all of the devices disclosed in these patents, the air entrained in the solution is vented to the atmosphere by passage through a hydrophobic filter. At the same time, air is prevented from flowing with the solution into the patient by passing the fluid through a hydrophilic filter immediately prior to infusion in the patient.
While all of these devices have a tendency to remove particulate matter, in that the hydrophilic filter is generally of a pore rating of 0.3 microns or less, none of these devices provide a filter dedicated to the removal of particulate matter. In fact, it is a problem of the prior art filtration devices that the hydrophilic filters contained therein, because of their small pore size, often clog as they are loaded with particulate matter. In addition, even though many of the prior art devices are position insensitive, there is still the problem of limited access to the means for venting entrained air to the atmosphere. Finally, because of the delicate nature of the hydrophilic filters employed in the prior art filter assemblies, there is a danger that one of these filters could rupture thus introducing a fatal quantity of air into the patient and also breaching the sterility protection of the patient.
There is thus a need for a filter assembly that comprises a primary filtration stage which both removes particulate matter and also vents the air contained in the liquid, coupled with a secondary filtration stage which both removes bacteria and vents any air remaining in the liquid. The present invention is directed towards filling that need.